1

I was able to successfully compile my Java source file as follows:

javac -cp ./algs4.jar BinarySearch
However, when I go and try to execute the program using
java BinarySearch it tells me that the class could not be found or loaded. I have even tried the following command
java -cp .:./algs4.jar BinarySearch and am still receiving the same exact message. I have already researched this problem on other forums but can't find a solution that works. Anyone know what's going on?

/******************************************************************************
 *  Compilation:  javac BinarySearch.java
 *  Execution:    java BinarySearch whitelist.txt < input.txt
 *  Dependencies: In.java StdIn.java StdOut.java
 *  Data files:   http://algs4.cs.princeton.edu/11model/tinyW.txt
 *                http://algs4.cs.princeton.edu/11model/tinyT.txt
 *                http://algs4.cs.princeton.edu/11model/largeW.txt
 *                http://algs4.cs.princeton.edu/11model/largeT.txt
 *
 *  % java BinarySearch tinyW.txt < tinyT.txt
 *  50
 *  99
 *  13
 *
 *  % java BinarySearch largeW.txt < largeT.txt | more
 *  499569
 *  984875
 *  295754
 *  207807
 *  140925
 *  161828
 *  [367,966 total values]
 *  
 ******************************************************************************/

package edu.princeton.cs.algs4;

import java.util.Arrays;

/**
 *  The {@code BinarySearch} class provides a static method for binary
 *  searching for an integer in a sorted array of integers.
 *  <p>
 *  The <em>indexOf</em> operations takes logarithmic time in the worst case.
 *  <p>
 *  For additional documentation, see <a href="http://algs4.cs.princeton.edu/11model">Section 1.1</a> of
 *  <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
 *
 *  @author Robert Sedgewick
 *  @author Kevin Wayne
 */
public class BinarySearch {

    /**
     * This class should not be instantiated.
     */
    private BinarySearch() { }

    /**
     * Returns the index of the specified key in the specified array.
     *
     * @param  a the array of integers, must be sorted in ascending order
     * @param  key the search key
     * @return index of key in array {@code a} if present; {@code -1} otherwise
     */
    public static int indexOf(int[] a, int key) {
        int lo = 0;
        int hi = a.length - 1;
        while (lo <= hi) {
            // Key is in a[lo..hi] or not present.
            int mid = lo + (hi - lo) / 2;
            if      (key < a[mid]) hi = mid - 1;
            else if (key > a[mid]) lo = mid + 1;
            else return mid;
        }
        return -1;
    }

    /**
     * Returns the index of the specified key in the specified array.
     * This function is poorly named because it does not give the <em>rank</em>
     * if the array has duplicate keys or if the key is not in the array.
     *
     * @param  key the search key
     * @param  a the array of integers, must be sorted in ascending order
     * @return index of key in array {@code a} if present; {@code -1} otherwise
     * @deprecated Replaced by {@link #indexOf(int[], int)}.
     */
    @Deprecated
    public static int rank(int key, int[] a) {
        return indexOf(a, key);
    }

    /**
     * Reads in a sequence of integers from the whitelist file, specified as
     * a command-line argument; reads in integers from standard input;
     * prints to standard output those integers that do <em>not</em> appear in the file.
     *
     * @param args the command-line arguments
     */
    public static void main(String[] args) {

        // read the integers from a file
        In in = new In(args[0]);
        int[] whitelist = in.readAllInts();

        // sort the array
        Arrays.sort(whitelist);

        // read integer key from standard input; print if not in whitelist
        while (!StdIn.isEmpty()) {
            int key = StdIn.readInt();
            if (BinarySearch.indexOf(whitelist, key) == -1)
                StdOut.println(key);
        }
    }
}

/******************************************************************************
 *  Copyright 2002-2016, Robert Sedgewick and Kevin Wayne.
 *
 *  This file is part of algs4.jar, which accompanies the textbook
 *
 *      Algorithms, 4th edition by Robert Sedgewick and Kevin Wayne,
 *      Addison-Wesley Professional, 2011, ISBN 0-321-57351-X.
 *      http://algs4.cs.princeton.edu
 *
 *
 *  algs4.jar is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  algs4.jar is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with algs4.jar.  If not, see http://www.gnu.org/licenses.
 ******************************************************************************/
2
  • Does BinarySearch declare a package? Commented Jul 11, 2017 at 19:04
  • @bradimus Posted the file Commented Jul 11, 2017 at 19:05

1 Answer 1

3

Your class is under the package edu.princeton.cs.algs4. That means the java file needs to be under the folder edu/princeton/cs/algs4

After you compile it there, try java -cp .:./algs4.jar edu.princeton.cs.algs4.BinarySearch

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3 Comments

This is a working answer. But at the same time, I am also curious to know if there is any method to avoid the fully qualified class name, as just running java BinarySearch tinyW.txt < tinyT.txt as suggested in the original code comment/sample?
You can declare your class without a package (having the root package) and then that would work. But while this is ok for a small exercise, in real software you'd want to avoid name conflicts, and that's where namespaces come in.
Thanks for the explanation, it makes perfect sense! So it is possible by modifying the original code (removing the package declaration, and instead import to make the compile/build work), however it is probably not a good idea in larger scale software project because of the name conflict potential.

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